Mercury - 25W-40 Synthetic Blend Marine Oil, 1 Qt. Lubrication 92-8M0078622. Overview. Four-stroke marine engines don't live an easy life. They idle forever, then jump straight into hard throttle, all while dealing with heat, humidity, and salt air. That's why the oil you run really matters. This 25W-40 synthetic blend is the kind of oil most mechanics keep on the bench-it hangs onto internal parts, stays stable when the engine gets hot, and gives the motor a smoother, easier feel. If you want y